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This study investigated the amorphous structure of a soda-lime-silicate glass sample (Na 2 O·2CaO·3SiO 2) utilizing in situ X-ray diffraction and Raman spectroscopy at pressures up to 30.3 GPa. These techniques provided insights into the structure of the glass under high pressure. Analysis of the short-range order of the glass in function of pressure was obtained from the pair distribution function, obtained from the diffractograms, and uncovered the emergence of a new amorphous phase at ∼10 GPa, identifiable through the appearance of new peaks in the data beyond this pressure value. Simultaneous measurements from Raman spectroscopy identified the elastic limit of the material at ∼6 GPa and were used to measure the inter-tetrahedral ∠Si–O–Si angle, which also displayed a ∂θ/∂P discontinuity within the 10 GPa range, due to the new amorphous phase. The study emphasized the potential of utilizing a monolithic glass sample within a diamond anvil cell, highlighting its ability to produce a sufficiently intense diffraction signal for structural analysis of glassy samples, provided that the angular aperture and energy employed are sufficiently high. [ABSTRACT FROM AUTHOR]

Electronic interactions of the Group 2A elements with magnesium have been studied through the dilute solid solutions in binary Mg-Ca, Mg-Sr and Mg-Ba systems. This investigation incorporated the difference in the ‘Work Function’ (ΔWF) measured via Kelvin Probe Force Microscopy (KPFM), as a property directly affected by interatomic bond types, i.e. the electronic structure, nanoindentation measurements, and Stacking Fault Energy values reported in the literature. It was shown that the nano-hardness of the solid-solution α-Mg phase changed in the order of Mg-Ca>Mg-Sr>Mg-Ba. Thus, it was shown, by also considering the nano-hardness levels, that SFE of a solid-solution is closely correlated with its ‘Work Function’ level. Nano-hardness measurements on the eutectics and ΔWF difference between eutectic phases enabled an assessment of the relative bond strength and the pertinent electronic structures of the eutectics in the three alloys. Correlation with ΔWF and at least qualitative verification of those computed SFE values with some experimental measurement techniques were considered important as those computational methods are based on zero Kelvin degree, relatively simple atomic models and a number of assumptions. As asserted by this investigation, if the results of measurement techniques can be qualitatively correlated with those of the computational methods, it can be possible to evaluate the electronic structures in alloys, starting from binary systems, going to ternary and then multi-elemental systems. Our investigation has shown that such a qualitative correlation is possible. After all, the SFE values are not treated as absolute values but rather become essential in comparative investigations when assessing the influences of alloying elements at a fundamental level, that is, free electron density distributions. Our study indicated that the principles of ‘electronic metallurgy’ in developing multi-elemental alloy systems can be followed via practical experimental methods, i.e. ΔWF measurements using KPFM and nanoindentation.

• SFE of a solid-solution is closely correlated with its 'Work Function' level. • KPFM measurements give reliable results for correlating SFE and ΔWF levels. • KPFM measurements can show how alloying elements change ΔWF between eutectic phases. • WF difference between eutectic phases indicate the bond strength between them. • Electronic changes due to SRO can be revealed via ΔWF and nanoindentation readings. Electronic interactions of the Group 2A elements with magnesium have been studied through the dilute solid solutions in binary Mg-Ca, Mg-Sr and Mg-Ba systems. This investigation incorporated the difference in the 'Work Function' (ΔWF) measured via Kelvin Probe Force Microscopy (KPFM), as a property directly affected by interatomic bond types, i.e. the electronic structure, nanoindentation measurements, and Stacking Fault Energy values reported in the literature. It was shown that the nano-hardness of the solid-solution α-Mg phase changed in the order of Mg-Ca>Mg-Sr>Mg-Ba. Thus, it was shown, by also considering the nano-hardness levels, that SFE of a solid-solution is closely correlated with its 'Work Function' level. Nano-hardness measurements on the eutectics and ΔWF difference between eutectic phases enabled an assessment of the relative bond strength and the pertinent electronic structures of the eutectics in the three alloys. Correlation with ΔWF and at least qualitative verification of those computed SFE values with some experimental measurement techniques were considered important as those computational methods are based on zero Kelvin degree, relatively simple atomic models and a number of assumptions. As asserted by this investigation, if the results of measurement techniques can be qualitatively correlated with those of the computational methods, it can be possible to evaluate the electronic structures in alloys, starting from binary systems, going to ternary and then multi-elemental systems. Our investigation has shown that such a qualitative correlation is possible. After all, the SFE values are not treated as absolute values but rather become essential in comparative investigations when assessing the influences of alloying elements at a fundamental level, that is, free electron density distributions. Our study indicated that the principles of 'electronic metallurgy' in developing multi-elemental alloy systems can be followed via practical experimental methods, i.e. ΔWF measurements using KPFM and nanoindentation. [ABSTRACT FROM AUTHOR]

In this work, we study vacancy energetics in the equiatomic Nb-Mo-Ta-W alloy, especially vacancy formation and migration energies, using molecular statics calculations based on a spectral neighbor analysis potential specifically developed for Nb-Mo-Ta-W. We consider vacancy properties in bulk environments as well as near edge dislocation cores, including the effect of short-range order (SRO) by preparing supercells through Metropolis Monte-Carlo relaxations and temperature on the calculation. The nudged elastic band (NEB) method is applied to study vacancy migration energies. Our results show that both vacancy formation energies and vacancy migration energies are statistically distributed with a wide spread, on the order of 1.0 eV in some cases, and display a noticeable dependence on SRO. We find that, in some cases, vacancies can form with very low energies at edge dislocation cores, from which we hypothesize the formation of stable 'superjogs' on edge dislocation lines. Moreover, the large spread in vacancy formation energies results in an asymmetric thermal sampling of the formation energy distribution towards lower values. This gives rise to effective vacancy formation energies that are noticeably lower than the distribution averages. We study the effect that this phenomenon has on the vacancy diffusivity in the alloy and discuss the implications of our findings on the structural features of Nb-Mo-Ta-W.

A great research effort is being employed in the development of Multi-Principal Element Alloys (MPEAs). The major interest on these alloys lies in the vast compositional field in which they exist, which provides a challenging opportunity for designing alloys with improved combinations of properties. Among the MPEAs produced to date, compositions containing large contents of Cr, Co and Ni, including the recently developed and well-studied Cr33Co33Ni33 alloy (in atomic %), are among the most promising for structural application due to their outstanding combination of strength and ductility. The present work is a critical review of some of the important publications on the topic. First, we give a brief history of the MPEA development in recent years highlighting the importance of CrCoNi alloys. Next, a brief explanation of the phase equilibria in this system is given. The third and major part of this work consists in a compilation followed by critical discussion of the main studies explaining the good mechanical properties of these alloys. This compilation includes what is known about grain refinement, solid solution strengthening, twinning and transformation induced plasticity and short-range ordering. The major controversies on the area are pinpointed as well as directions for future research. Several other CrCoNi alloy properties are also reviewed, including what has been published on wear, fatigue, corrosion, oxidation and hot deformation. High Cr-containing alloys have excellent combinations of strength, ductility, corrosion (in saline environments) and oxidation resistance, surpassing some of the best performing Ni-superalloys.

Face-centered cubic (fcc) high and medium entropy alloys (H/MEAs) have been shown to display superior mechanical properties at low temperatures, but significant improvement of their strength at high temperatures is required for industrial applications at extreme conditions. Recently, it has been shown that the breakthrough of the MEAs from equiatomic/near-equiatomic to non-equiatomic ratios leads to strong MEAs with good ductility. To design new H/MEAs, we consider two important factors that may influence strength: the chemical composition and chemical short range order (CSRO). In this study, we investigate the depinning stress (σc) as a criterion of strength of several compositions of VCoNi concentrated solid solution alloys (CSSAs) including V0.33Co0.33Ni0.33, V0.35Co0.2Ni0.45, V0.33Co0.17Ni0.5, and V0.17Co0.33Ni0.5 at 5 K and 300 K, using atomistic simulations. The chosen interatomic potential is shown to be reliable by comparing experimental/ab initio values and calculated parameters such as lattice constant, shear modulus, depinning stress, and temperature variation of stacking fault width for equimolar VCoNi. We find a good agreement between experimental friction stress and the depinning stress extracted from our results for equimolar VCoNi. Also, we find that Vclusters are the main pinning points of dislocations, and With a random distribution of atoms, we find that the alloy composition V0.33Co0.17Ni0.5 displays the largest depinning stress at both 5 and 300 K. Furthermore, to investigate how CSRO affects the strength of these alloys, we design CSRO into the microstructure using two different methods: In the first method, hybrid Molecular-dynamics/Monte-Carlo simulations were employed to simulate annealing at various temperatures. We observe that such simulations create CSRO so that it increases with decreasing annealing temperature. Recently, the CSRO motif and its concentration in an equimolar VCoNi have been determined by experiment. By modeling this experiment, we also implemented the CSRO into microstructure as the second method. By using both methods, the effect of CSRO on the magnitude of the depinning stress is discussed. It was shown that in both methods, CSRO significantly influences the strength of non-equimolar VCoNi alloys.

Owing to the unique elemental character, Vanadium (V) has recently gained growing interest in the field of high entropy alloys. It is known that V benefits in the mechanical strength in alloys, accompanying by the unique elemental distribution behaviors. In this work, we concentrate on the mechanism of V's distribution characters in VFeCoNi, which is similar to that of Cr in CrFeCoNi, by evaluating element inherent electronegativity, charge transfer, atomic volume, Voronoi volume and the atomic stress resulting from the combined effects of these factors. Another unique character of electronic interaction in the t 2g and e g orbitals has been observed, which contributed to the fluctuation of atomic volume, thus enhancing solid solution strengthening. The tensile stress-strain tests show that the chemical ordering of V enhanced mechanical strength, especially for the grain boundary. Our work will provide new insights into the nanoscale distribution of V elements and the related macroscopic mechanical effects. [Display omitted] • V atoms exhibit a preference for sublattice sites. • Negative atomic stress of V atoms leads them tooccupy second-nearest neighboring sites. • V features the d electron flexibility. • Chemical ordering of V enhances mechanical properties. [ABSTRACT FROM AUTHOR]

The recent development of high-entropy alloys (HEAs) has opened a new avenue for alloy design by incorporating multiple principal elements into a simple crystal lattice. In HEAs, short-range chemical ordering may arise due to the different mixing properties of various constituent elements. In this work, we explore the trend of elemental arrangement in five typical body-centered cubic (BCC) multi-principal element alloys (MPEAs), including CrFeV, HfNbZr, TaVW, NbTaV, and TaTiV. Combining the Monte Carlo method and density-functional theory calculations, we calculated the evolution of short-range order (SRO) parameters in these alloys at 500 K. Our results demonstrated that all these MPEAs might develop a certain degree of SRO, depending on the mixing properties of different element pairs. Using a modified quasi-chemical model, we show that the SRO values in these MPEAs can be accurately predicted as long as the mixing enthalpy values between different atomic pairs are known. The presence of SRO has a profound impact on the local structure of MPEAs, which further alters the electronic and elastic properties of MPEAs. Our results provide a theoretical understanding of the basic alloy structure of novel MPEAs, which is an essential step toward tailoring their properties. [ABSTRACT FROM AUTHOR]

In this work, we study vacancy energetics in the equiatomic Nb-Mo-Ta-W alloy, especially vacancy formation and migration energies, using molecular statics calculations based on a spectral neighbor analysis potential specifically developed for Nb-Mo-Ta-W. We consider vacancy properties in bulk environments as well as near edge dislocation cores, including the effect of short-range order (SRO) by preparing supercells through Metropolis Monte-Carlo relaxations and temperature on the calculation. The nudged elastic band (NEB) method is applied to study vacancy migration energies. Our results show that both vacancy formation energies and vacancy migration energies are statistically distributed with a wide spread, on the order of 1.0 eV in some cases, and display a noticeable dependence on SRO. We find that, in some cases, vacancies can form with very low energies at edge dislocation cores, from which we hypothesize the formation of stable ‘superjogs’ on edge dislocation lines. Moreover, the large spread in vacancy formation energies results in an asymmetric thermal sampling of the formation energy distribution towards lower values. This gives rise to effective vacancy formation energies that are noticeably lower than the distribution averages. We study the effect that this phenomenon has on the vacancy diffusivity in the alloy and discuss the implications of our findings on the structural features of Nb-Mo-Ta-W.

The composition dependence of the lattice constant, a , in A x B 1- x O 2-0.5 x V 0.5 x , fluorite-type solid solutions (B = Zr, A = {Nd-Yb, Y}, V = oxygen vacancy) is characterized by changes in slope at x ~ 1/3, which cannot be described by existing models. Moreover, over the range of 0.15 ≤ x ≤ 1/3 the a vs. x data on all systems can be fitted with a linear equation, a = q + rx , with the same intercept, q , however, over the range of 1/3 ≤ x ≤ 1/2 the data bifurcate requiring different intercepts for A={Nd-Gd] and for A={Dy-Yb,Y} systems, implying steeper slopes for the first group. An adequate description is achieved via close-packing models involving two anion species, O2- and V, and three combinations of cation species, namely 8A, 7B, 8B (0 ≤ x ≤ 1/3), 7A, 8A, 7B (1/3 ≤ x ≤ 1/2) and 8A, 6B, 7B (1/3 ≤ x ≤ 1/2), that take into an account the constraint on the average coordination number, K (x), of K (x) = 8 – 2 x and two additional short-range order (SRO) constrains referring to vacancy-vacancy avoidance and vacancy-to-Zr association. The consistent fit to a vs. x data with these models requires the effective size of the oxygen vacancy to be larger than the radius of the oxygen anion by ~11%. The latter observation seems to play an important role in the understanding of structure-property relationships in A x B 1- x O 2-0.5 x V 0.5 x systems. Average coordination numbers of A and B cations in A x B 1- x O 2-0.5 x solid solutions (B = Zr; A = Ln , Y) deviate from the total average coordination number, K = 8 − 2 x , due to cation-vacancy association effects. Two contrasting solutions to the total average seem to exist within the range of 1/3 < x < 2/3. Image, graphical abstract [ABSTRACT FROM AUTHOR]

In the present communication, the structural, microstructural, dielectric, and electrical (impedance, conductivity, polarization) characteristics of a new member of the Aurivillius family (Bi 2 YSnVO 9), processed through a high-temperature solid-state reaction method, have been reported. The formation and content of the compound at room temperature have been analyzed by using X-ray diffraction, Raman spectra, and energy dispersive X-ray spectrum. Analysis of frequency and temperature dependence of impedance and electrical modulus spectroscopic data and Nyquist plots has shown the contributions of grains and grain boundaries to the electrical properties of the prepared material. Detailed dielectric characterizations carried out in a broad spectrum of temperature and frequency have helped to explain the polarization and relaxation mechanism of the sample. The appearance of a hysteresis loop at room temperature and an increasing trend of dielectric constant with temperature to get expected peak at high temperature suggests the existence of ferroelectricity in the material, as of other members of the family. The activation energy of the sample is estimated as 1.19 eV which implies the activation of doubly ionized oxygen vacancy and the electrons released conduct via correlated barrier hopping mechanism. [ABSTRACT FROM AUTHOR]

In order to facilitate the understanding of the current research efforts and directions, this article first introduces the anomalous/problematic features of magnesium (Mg) and presents the recent approach of stacking fault energy (SFE)–based alloying element selection to lessen or eliminate this problem. Stacking fault energy computations via ab initio techniques necessitate an understanding of the free electron density distribution around atoms in a solid solution. Therefore, the assessment of the role of atoms by also considering the possibility of short range order (SRO) formation rather than a random solid solution has been revisited. Two possible types of SRO have been indicated. The relevant electronic interactions between the host Mg and the alloying element atoms are more clearly incorporated in a generally less known model by Miedema based on atomic-level thermodynamics rather than in Hume–Rothery rules. This more successful approach has also been addressed here. An evaluation founded on these premises, introducing the relatively more recent Mg alloy systems, has been given in terms of their achievements toward healing the problematic features of Mg alloys. The spectrum of alloy systems discussed ranges from doping of Mg to dilute alloy systems and to some rich alloy systems that offer remarkable properties. Among the first category, an unorthodox addition, doping with oxygen, and its implications, has been presented. The dilute alloy systems and their compositional design based on SRO and SFE together with their potentials have been reviewed. Among the rich alloy compositions, the most interesting precipitate systems, that is, the ones involving order and intermetallic formations, long-period stacking order phases, and quasi-crystals, have been discussed. Among all the alloying elements, one that deserves particular attention, calcium, with its implications such as being economical, offering environmentally friendly Mg metallurgy, and remedial effects on the shortcomings of engineering properties, and a closely related issue of calcium oxide (CaO) addition have been scrutinized. This article also makes an attempt to point out the future directions throughout the text, whenever possible.

Directional elastic peak electron spectroscopy (DEPES) was used to reveal a short range order within the near-surface region of Pt(111). Experiments were performed at primary electron beam energies in the range from 0.9 keV to 1.8 keV. DEPES signal was recorded for a wide range of polar θ and azimuthal ø angles and then transformed to two-dimensional DEPES maps using stereographic projection. Theoretical DEPES distributions were obtained with the application of the multiple scattering (MS) theory. In MS calculations, the following parameters were varied: the inelastic mean free path λ, the radius around the emitter Rmax and the cones of smoothing M. The comparison of experimental and theoretical DEPES maps was performed by an R-factor analysis in order to find the best correspondence between the recorded and calculated distributions. The absolute minimum of the R-factor was found at rather small values of the radius around the emitter and large inelastic mean free paths. However, the obtained minimum was very shallow and took the form of a characteristic band in the Rmax(l) plots. Thus, other Rmax and λ values corresponding to the local R-factor minimum can also be to some extent used in computations. The cone of smoothing, which reflects the spread of primary beam directions before it strikes the sample, decreases at larger electron energies which scales with better electron focusing at larger Ep values. The discussion concerns the computation time associated with the mentioned parameters and the convergence of theoretical data. [ABSTRACT FROM AUTHOR]

The configurational entropy of mixing was calculated on the basis of the experimental diffraction data of melts of intermediate phases of Cu-In, Bi-Te, Fe-Ge, Ni-In and Bi-Tl systems. The entropy determined in such a way is the difference between the entropy of the melt and the one of an ideal gas of the same atoms being a measure of the degree of ordering of the melt. This value is in fact the excess entropy and differs from the classical definition of configurational entropy for crystals, defined as the difference between total entropy and its vibrational contribution. This approach was used to calculate such a configurational contribution to entropy in the case of one-component melts, but we tried to use it to study two-component melts too, replacing them by effective one-component liquids. Configuration entropy indicates the deviation of the topology of the real atomic distribution from the distribution in the gas of the same atoms, and in the case of binary melts, we have calculated the degree of deviation of the structural state of the melt from the structure of an ideal atomic solution. For a melt with an average atomic distribution, the excess configuration entropy is close to zero, and in the case of significant changes in the atomic distribution during the formation of the melt, it will be different. The transformation of the structure during the melt formation is accompanied by both a change in the interparticle interaction and the topology of the atomic distribution in comparison with the pure components, and these changes will be displayed in the experimental pair correlation function and hence in the configurational entropy of mixing. The concentration dependence of the excess configurational entropy within the concentration range corresponding to the existence of intermediate phases of the studied systems is characterized by minimal values and increases within concentration intervals in which eutectics and atomic solutions exist, that is the evidence of its correlation with equilibrium diagrams of the studied systems. [ABSTRACT FROM AUTHOR]

Fictive associates are widely used to describe and model liquid phases with strong ordering trends. However, little evidence is known about the assumed associates in most cases. In the present work, an ab initio molecular dynamics (AIMD) study is employed to investigate the characters of the Ba-Bi liquid, in which associates have been assumed in existing thermodynamic modeling. It is found that in the Ba rich melt, the Bi atoms are almost completely surrounded by Ba atoms. The Bi-centered coordination polyhedrons are strongly associated to crystalline structures of Ba 5 Bi 3 and Ba 4 Bi 3 with a longer lifetime than other polyhedrons during the AIMD simulations. In addition, these Bi-centered polyhedrons in Ba rich melt connect with each other through vertex, edge, face, and/or bipyramid sharing to form medium range orders (MRO). In the Bi rich melt, the Ba-centered polyhedrons also form MROs, but they are both structurally and compositionally diverse with a shorter lifetime. These findings from AIMD study provide evidences that there exist a strongly ordering Ba 4 Bi 3 associate and a weakly ordering BaBi 3 associate in the Ba-Bi liquid. The predicted enthalpy of mixing in the liquid agrees well with the results by the CALPHAD modeling in the literature. Snapshots of AIMD configurations for some connected Bi- and Ba-centered coordination polyhedrons in molten Ba 1- x Bi x with x = 0.025 (a), 0.05 (b), 0.10 (c), 0.90 (d), 0.95 (e), and 0.975 (f). The green and purple spheres represent Ba and Bi atoms, respectively. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The coordination difference between the unprotonated tertiary structures of a native (Tax) peptide and a number of its variants – all peptides presented by HLA-A201 and bound to the human A6 T cell receptor-was discovered to constitute a metric of pMHC–TCR functional avidity. Moreover, increasing coordination deviations from the index were found to flag correspondingly weakening immunological outcomes of the variant peptides. The prognostic utility of the coordination difference of unprotonated tertiary structure was established to operate strictly on the peptide scale, seizing to be of relevance either to the immediate peptide environment (i.e. within the realm of peptide short range order, within 7 Å of any peptide atom) or over the entirety of the pMHC–TCR complex. Additionally, the imprint of peptide immunological identity was expressed both by the total coordination as well as by its C–C partial.

Interaction between 2, 3, 5 and 7 atomic layers of gold and a (111) silicon surface was investigated with the molecular dynamics simulation method. The simulation of the diffusion interaction between gold and silicon in the temperature range 425–925 K has been carried out. The peculiarities of the concentration changes of the interacting components and the atomic density at the boundary of two phases in the direction perpendicular to the crystalline surface were established. By means the formalism of quasi two dimensional partial pair correlation functions the atomic structure of the diffusion region was analyzed. The formation of the alloy of eutectic composition within the gold-silicon interlayer was established. It was shown that the inter-phase mixing in various temperature intervals occurred according to different diffusion mechanisms.

The atomic environment and stability of an amorphous Cr25Nb75 alloy was studied on the basis of average atomic coordination, average cluster number density as well as cluster radial distribution of these quantities based on Reverse Monte Carlo fitting of multiple total scattering datasets. A number of the most representative clusters of the RMC supercell were isolated and relaxed via Density Functional Theory. Average coordination of both Cr and Nb atoms was similar, possibly due to the similarity of their covalent radii. Also, the histograms of average coordination of both species suggested binomial distributions, possibly reflecting two separate modes of atomic bonding. Cr-centered clusters were found to be more cohesive than Nb-centered ones and overall cluster stability appeared to be correlated to minority Cr valence populations.

A study of molten Ni 1−x M x (M = Ta, W, Re, Os, Nb, Mo, Ru, Ti or Cr) at 1773 K was carried out by ab initio molecular dynamics simulation. Static structure factors, pair correlation functions and bond-angle distribution functions were calculated. Chemical short range order, the structure of coordination short range order (SRO), compactness of coordination shell and electronic density of states were studied. Hetero-coordination is preferred in molten Ni 1−x M x (M = Ta, W, Re, Nb, Mo, Ti or Cr), while, self-coordination is preferred in molten Ni 1−x Os x and Ni 1−x Ru x . The affinity between unlike species in molten Ni 1−x M x is decreasing with solute species shifting to the right in the periodic table. The structure difference between M- and Ni-centered coordination SROs is narrowed when solute species shifts to the right in the periodic table. With an increase of solute concentration, the affinity between bonding Ni-M and Ni-Ni atomic pairs both decrease, the solute and solvent centered coordination shells both become looser, in general. The structures of locally favored coordination SROs in molten Ni 1−x M x are diversified and independent of the structure of crystal state. Few FCC- and HCP-type coordination SROs are found in these melts. No BCC type coordination SRO is detected. For these melts, the compactness difference of solute- and solvent-centered coordination shells is correlated with the equilibrium partition coefficients, k 0 , of solute elements. Namely, when the solute centered coordination shell is averagely denser than the Ni centered one, k 0  < 1, vice versa. Our findings shed light on understanding the nature of segregation from the aspect of molten structure at atomic scale. [ABSTRACT FROM AUTHOR]

Element clustering and structural features of liquid lead-bismuth eutectic (LBE) alloy have been investigated up to 720 °C by means of high temperature X-ray diffraction (HT-XRD), X-ray Photoemission Spectroscopy (XPS) and Scanning Photoemission Microscopy (SPEM) at the Elettra synchrotron in Trieste. The short-range order in liquid metal after melting corresponds to the cuboctahedral atomic arrangement and progressively evolves towards the icosahedral one as temperature increases. Such process, that involve a negative expansion of the alloy, is mainly connected to the reduction of atom distance in Pb−Pb pairs which takes place from 350 °C to 520 °C. On an atomic scale, it is observed a change of the relative number of Bi−Bi, Pb−Pb, and Pb−Bi pairs. The Pb−Bi pairs are detected only at a temperature above ~350 °C, and its fraction progressively increases, giving rise to a more homogeneous distribution of the elements. SPEM results showed evidence that the process of chemical homogenization on an atomic scale is preceded and accompanied by homogenization on micro-scale. Clusters rich of Bi and Pb, which are observed after melting, progressively dissolve as temperature increases: Only a few residuals remain at 350 °C, and no more clusters are detected a 520 °C.

The icosahedral short-range order and medium-range order of Zr 50 Cu 50 and Zr 50 Cu 40 Al 10 metallic glasses have been investigated by molecular dynamics simulations. Our analysis shows that, although the replacement of a few percent of Cu by Al enlarges the population of full icosahedra (FIs), the degree of interpenetrating aggregation for FIs is reduced which might be caused by the strong avoidance of Al-centered FIs in the ternary system. However, this fact does not mean the weakness of icosahedral medium range order in Zr 50 Cu 40 Al 10 metallic glass. If the interpenetrating and non-interpenetrating connections are both considered, the largest super-cluster formed by the connected FIs in Zr 50 Cu 40 Al 10 is rather larger than that in Zr 50 Cu 50 , which might play an important role in slowing down the kinetics and thus enlarge the glass-forming ability. [ABSTRACT FROM AUTHOR]

Various low temperature treatments of NiTi have shown an unexpected effect on the martensitic start temperature. Periodic diffuse intensity distributions in reciprocal space indicate the formation of short pure Ni strings along the 111 directions in the B2 ordered lattice, precursing the formation of Ni4Ti3 precipitates formed at higher annealing temperatures. [ABSTRACT FROM AUTHOR]

We demonstrated that the immunological identity of variant peptides may be accurately predicted on the basis of atomic coordination of both unprotonated and protonated tertiary structures, provided that the structure of the native peptide (index) is known. The metric which was discovered to account for this discrimination is the coordination difference between the variant and the index; we also showed that increasing coordination difference in respect to the index was correlated to a correspondingly weakening immunological outcome of the variant. Additionally, we established that this metric quickly seizes to operate beyond the peptide scale, e.g. over a coordination shell inclusive of atoms up to a distance of 7 Å away from the peptide or over the entire pMHC-TCR complex. Analysis of molecular orbital interactions over a range of formal charges further revealed that the N-terminus of the agonists was always able to sustain a stable ammonium (NH3+) group which was consistently absent in antagonists. We deem that the presence of NH3+ constitutes a secondary observable with a biological consequence, signifying a change in T cell activation. While our analysis of protonated structures relied on the quantum chemical relaxation of the H species, the results were consistent over a wide range of peptide charge and spin polarization conditions.

Magnesium (Mg) alloys with low concentrations of rare earth additions are known to exhibit strengths and ductility that are significantly higher than those obtained in traditional Mg alloys. However, the mechanisms that underlie these improvements are still open to debate. We assessed these mechanism(s) by carrying out in-depth analysis of the deformation behavior in single crystals of pure Mg and a homogenized Mg-0.75 at.% Gd alloy oriented for twinning, pyramidal- and basal-slip. We observed a fivefold increase in basal CRSS, an eightfold increase in twinning CRSS and a fourfold decrease of the pyramidal/basal CRSS (P/B) ratio due to Gd addition. We also observed that while twinning and pyramidal slip activities were similar in the two material systems, basal slip was radically different. Specifically, basal slip was planar in the alloy but wavy in pure Mg. Our work reveals that these observations are a consequence of Gd-rich short-range ordered (SRO) clusters in the alloy. We show that interactions between dislocations and the SRO clusters would lead to significant increases in strength and 〈 c + a 〉 slip activity, and consequently, ductility improvements in homogenized polycrystalline Mg-Gd alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

A combination of atomic correlation statistics and quantum chemical calculations are shown to predict biological function. In the present study, various antigenic peptide-Major Histocompatibility Complex (pMHC) ligands with near-identical stereochemistries, in complexation with the same T cell receptor (TCR), were found to consistently induce distinctly different quantum chemical behavior, directly dependent on the peptide’s electron spin density and intrinsically expressed by the protonation state of the peptide’s N-terminus. Furthermore, the cumulative coordination difference of any variant in respect to the native peptide was found to accurately reflect peptide biological function and immerges as the physical observable which is directly related to the immunological end-effect of pMHC-TCR interaction.

Due to its excellent glass-forming ability (GFA), the Zr48Cu36Al8Ag8 bulk metallic glass (BMG) is of great importance in glass transition investigations and new materials development. However, due to the lack of detailed structural information, the local structure and atomic packing of this alloy is still unknown. In this work, synchrotron measurement and reverse Monte Carlo simulation are performed on the atomic configuration of a Zr-based bulk metallic glass. The local structure is characterized in terms of bond pairs and Voronoi tessellation. It is found that there are mainly two types of bond pairs in the configuration, as the body-centered cubic (bcc)-type and icosahedral (ico)-type bond pairs. On the other hand, the main polyhedra in the configuration are icosahedra and the bcc structure. That is, the bcc-type bond pairs, together with the ico-type bond pairs, form the bcc polyhedra, introducing the distortion in bcc clusters in short range. However, in the medium range, the atoms formed linear or planar structures, other than the tridimensional clusters. That is, the medium-range order in glass is of 1D or 2D structure, suggesting the imperfect ordered packing feature. [ABSTRACT FROM AUTHOR]

Experimental structural data for liquid Bi were used for estimation of the main structure parameters as well as the thermal expansion coefficient both in supercooled and superheated temperature ranges. It was shown that the equilibrium melt had a positive thermal expansion coefficient within a temperature range upon melting and a negative one at higher temperatures. The former was related to structure changes upon melting, whereas the latter with topologic disordering upon further heating. It was found that the superheated melt had a negative thermal expansion coefficient. The results obtained from structural data were compared with the thermal expansion coefficient calculated from the data of density for liquid Bi. [ABSTRACT FROM AUTHOR]